Not applicable.
1. Field of the Invention
This invention relates to a composition for preparing polyurethane foams with improved dimensional stability. This invention further relates to a composition for preparing a polyurethane in a wet environment. This invention further relates to a method for strengthening and sealing voids and geological formations which are moist or contain water. This invention further relates to a method for repair, restoration and rehabilitation of earth supported concrete slabs and other structures by the subsurface formation of polyurethane foams.
2. Description of the Related Art
Due to the mandated elimination of fluorocarbons and hydrochlorofluorocarbons, the polyurethane foam industry is seeking alternate blowing agents. The non-reactive chemicals under consideration as replacements are hydrofluorocarbons, pentane, and other products currently under development. Water is currently used as a blowing agent for polyurethane foams, either as the sole blowing agent, or as a co-blowing agent in the presence of another blowing agent. The isocyanate (xe2x80x94NCO) reacts with the water (Hxe2x80x94Oxe2x80x94H) to create a urea with carbon dioxide (CO2) as a byproduct of the reaction. The CO2 gas, when trapped in the reacting mass of polyurethane, expands the polyurethane to lower the density and form the foam structure.
Water is useful in the production of open cell flexible foams and rigid polyurethane foams. When water is used as the sole blowing agent in rigid, closed cell foams having a density of less than about 4 lbs/ft3, the foams are not dimensionally stable due to loss of gas pressure after the foam has set. Dimensional stability is a measure of the amount of volumetric change a foam undergoes on standing. Dimensional stability may be measured using specific ASTM standard methods such as D 2126-87. The loss of gas pressure is due to the escape of the CO2 from the cell, and the resultant negative pressure within the cell results in shrinkage. This shrinkage may be significant. For example, a 2 lbs/ft3 all water blown foam sample cut in a 2xe2x80x3 cube may shrink to approximately half its original volume and have a prune-like appearance. One currently accepted method to increase dimensional stability is to increase the density of the polyurethane foam until the foam is stable, i.e., does not shrink significantly from loss of carbon dioxide.
The polyisocyanate component of polyurethane foam forming compositions is reactive with water. Reaction of the polyisocyanate with water converts some of the polyisocyanate into the corresponding amine. The amine can react with the polyisocyanate to form a polyurea with properties that may be undesirable and inferior to the polyurethane foam formed in the absence of the amine. Excluding water during a polyurethane foam forming reaction is not always practical. For example, injection of polyurethane foam forming components into the ground to alleviate subsidence can be affected by moisture in the ground. Although some methods are known which attempt to reduce the problems caused by undesired reactions of excess water with polyisocyanates, these methods have disadvantages.
Formation of a polyurethane in the presence of water has been accomplished in U.S. Pat. No. 4,761,099 by substantially removing the water by first injecting a polyisocyanate which is followed by a subsequent injection of a mixture of polyol and polyisocyanate. The first injection of polyisocyanate is believed to form, upon reaction with water, a polyurea. The polyurea reacts further with the polyisocyanate and polyol and is incorporated into the polyurethane. This two step process will give poor results if the first injection of polyisocyanate is insufficient to react with all of the water present. Further, the incorporation of the polyurea may result in inferior properties in the subsequently formed polyurethane.
Other methods to strengthen geological formations, described in U.S. Pat. No. 4,792,262, use polyols that are fat derivatives such as castor oil. These systems have poor compatibility with the polyisocyanate, have long curing times, react with water present in the formation, and are relatively expensive.
Water-blown polyurethane foam forming systems may be dimensionally unstable and very sensitive to water in excess of the amount needed to form the carbon dioxide blowing agent. Since isocyanate groups react with water, the process of reacting polyisocyanates in the presence of excess water is generally prohibitive. When a polyurethane forming mixture contacts water, the polyisocyanate reacts first, i.e., faster, with water, creating an amine that may react further with the remaining polyisocyanate to form a urea. The isocyanate thus reacted is not available to react with the polyol to form the urethane linkage. One way to compensate for the water reaction is to pre-polymerize the polyisocyanate, thereby reducing the available NCO groups. This process has the disadvantage of increasing the viscosity of the mixture prior to the final polyurethane foam forming reaction.
Another method to compensate for the reaction of the polyisocyanate with water is to increase the reactivity of the polyisocyanate or the polyol. This is done to form the urethane linkages before the water interferes with the polyurethane foam forming reaction. This has the disadvantage of decreasing the amount of time before the polyurethane viscosity increases to a point at which it will no longer flow as a liquid. This reduces the amount of time in which the polyurethane forming composition must be completely injected into a void to be filled or into a substrate to reduce or eliminate earth subsidence, water seepage or into a substrate to stabilize and/or compact the substrate.
A need exists for a polyurethane foam forming composition for forming a low density water-blown polyurethane foam with good dimensional stability. Also, a need exists for a polyurethane foam forming composition for forming a low density water-blown polyurethane foam with good dimensional stability in the presence of water in excess of the amount of water needed to form carbon dioxide as the blowing agent.
A need exists for a polyurethane foam forming composition for forming a nonwater-blown polyurethane foam with good dimensional stability in the presence of water.
A need exists for an improved polyurethane foam forming composition suitable for subsurface injection to stabilize or reduce earth subsidence beneath a concrete slab or other structure.
A need exists for a diluent or additive for use with a polyurethane foam forming composition for forming a polyurethane foam that retards reaction of a polyisocyanate with water in the environment.
A need exists for a method of reducing or stabilizing earth subsidence of concrete slabs or other structures by subsurface injection of an improved polyurethane foam forming composition for forming water-blown polyurethane foam with good dimensional stability in the presence of excess water beyond that needed to generate the carbon dioxide blowing agent.
A need exists for an improved method for forming water-blown polyurethane foam with good dimensional stability in the presence of water in excess of the amount of water needed to form carbon dioxide as the blowing agent.
A need exists for a method for forming a nonwater-blown polyurethane foam with good dimensional stability in the presence of water.
Polyisocyanates and polyols may react together in the presence of water to form a polyurethane. The water reacts with some of the polyisocyanate to generate an amine and carbon dioxide. As the amine and polyol react with the polyisocyanate, the mixture begins to gel and the carbon dioxide causes the reactive mixture to form a foam. Generally, water is more reactive with a polyisocyanate than is a polyol and an excess amount of water causes the formation of an excess of the desired carbon dioxide and amine which leads to an inferior, undesirable polymeric material. The present invention provides an improved polyurethane foam forming composition and a method of using the improved polyurethane foam forming composition which permits the formation of a polyurethane by the reaction of a polyisocyanate and polyol, even in the presence of an amount of water in excess of the amount needed to generate carbon dioxide as a blowing agent.
One embodiment according to the present invention is a polyurethane foam forming composition comprising a polyisocyanate, a polyol, a blowing agent and a substantially water insoluble diluent that is substantially unreactive with a polyisocyanate.
One embodiment according to the present invention is a polyurethane foam forming composition comprising a polyisocyanate, a polyol, a blowing agent and a substantially water insoluble ester diluent that is substantially unreactive with the polyisocyanate.
One embodiment according to the present invention is a polyurethane foam forming composition for forming a low density polyurethane foam, having good dimensional stability, comprising a polyisocyanate, a polyol and a substantially water insoluble ester diluent that is substantially unreactive with the polyisocyanate.
One method of preparing the polyurethane foam according to the present invention includes mixing the polyisocyanate or the polyol or both in a substantially water insoluble diluent prior to or simultaneously with the mixing of the polyisocyanate and polyol to form the polyurethane foam.
One embodiment of the present invention is a polyurethane elastomer forming composition having a substantially water insoluble and substantially non-reacting diluent which permits the formation of the elastomer in the presence of water.
One embodiment according to the present invention is a method of stabilizing, correcting or reducing ground subsidence by introducing a polyurethane foam forming composition having a substantially non-reactive and substantially water insoluble diluent into the area of subsidence.
One embodiment according to the present invention is a method of stabilizing, correcting or reducing ground subsidence by introducing a polyurethane foam forming composition, into the area of subsidence, having a substantially non-reactive and substantially water insoluble diluent, a polyisocyanate, a polyol and a blowing agent.